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Missfire on idle


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Wonder if anybody could have a look at my log and guide me in the right direction what is causing the small missfires that you could see when lambda running lean.

This a under a very short time but you certainly feel them and I been trying to understand why they occur.

The car is a Audi S6 with 5 cylinder 20 valve. The original engine block has been replaced by a diesel block from the 2,5 TDI. Many things in the engine are new, pistons, bearing and so on.

Original cams and intake manifold. The head has been renovated and slightly ported by a professional engine tuner. Now its running  with e-throttle.



Log 2017-12-25 3;28;33 pm.llg

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Based on the log and the attached cal file, it appears there may be something a miss in your ethrottle set up. 

If you look at the AP% main it looks like you are sitting there blipping the throttle the entire time during the log and the ethrottle is reacting and opening the throttle as it should when it sees throttle pedal input.

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Thanks for fast respons.

Actually I'm blipping the throttle randomly. But between these you could see the throttle and pedal untouched and still lambda readings above 1 just like a missfire.

See at file time 8.40.525 where lambda pops up to 1.02.

Can't claim that the tuning of the throttle is finished, but at least at that point the engine seems to just missfire for no reason.

For info I'm having NKG bcpr7es spark plugs with 0.5 mm between the electrodes. Running E85 in the summer but now it runs on petrol 98 RON (not shore on the RON but here in Sweden this is the highest octan petrol)

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Lambda looks pretty solid in all areas except where you are blipping the throttle. 

You could always richen up idle a bit via the AFR target table  and some slight massaging of the main fuel table.  

I have even setup the latency table to be 3d with battery voltage on one axis and rpm on the other and played with latency at idle to get the idle a bit smoother in the past.

I don't think that it is actual misfire.  I think you have a bit more tweaking to do in order to get it optimal for your preferences.


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based on the cal the that you loaded, you have only set the 0 rpm column to .96 lambda.  That will do nothing for you at idle considering that your idle speed is roughly 900rpm.

You will need to set that value from zero to at least 1000 rpm and span that from 20kpa to at least 60kpa as the idle MAP is roughly 50kpa.

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Hi, I have been looking into this as I spent a lot of time refining my idle control.  I'm not an expert, but here's some comments for consideration:

1.  The idle ignition table has an ignition timing of 8 degrees at zero idle error.  I think this should match the main ignition timing table of 12 degrees at idle rpm.  This is to give a smooth transition between the two tables.

2. The fuel table has 14.0% in the top left block, is this for the purpose of diagnosing this fault (it looks unusual).

3. At the point in the datalog that you mentioned (8.40.525) the idle rpm drops before the lambda goes lean.  Does this suggest that the lambda 'glitch' is a result of some other event (or engine load) rather than the cause of it?

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Thanks TimmyD for your comments and input!

1. Yes you are absolutely right about that.

2. I guess the engine must have what it wants. I'm not ready with the tune yet so maby this number will change.

3. I also noticed that the engine speed was slightly on the low side but it wasn't any load on the engine such as cooling fan or power steering. And if so I guess that the lambda value should "change" over a longer time and not like a glitch.

Maby the NGK spark plugs isn't optimal for this engine with petrol, wild guess...

The search for the perfect idle continues ;)

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